1. Field of the Invention
The present invention relates to an image pickup apparatus, and particularly to an image pickup apparatus having a focus detection function.
2. Description of Related Art
Conventionally, one method of focus detection in an image pickup apparatus such as cameras is a phase difference detection method. An auto-focus (hereafter referred to as AF) function is realized in an image pickup apparatus such as digital cameras by using a sensor for detecting a phase difference. A focus detection function refers to a function of detecting a focus position of an optical imaging system with respect to an object in an image pickup apparatus.
For example, as modern image pickup apparatuses become more digitized, a type of apparatus that detects a phase difference by utilizing a plurality of pixels in an image pickup device for photographing an object has been proposed as disclosed in Japanese Patent Application Laid-Open Publication No. 2009-217252. That is, image pickup and focus detection are simultaneously performed by disposing pixels for focus detection in addition to normal pixels for photographing in the image pickup device.
The image pickup apparatus relating to the proposal exploits some of the pixels of the image pickup device for picking up images of an object as a plurality of pixel pairs for detecting a phase difference, thereby obviating the need of a sensor for focus detection. The plurality of pixel pairs for focus detection are disposed in an alternate and discrete manner on the image pickup device, and are disposed so as to receive only the light flux that has passed through predetermined two pupil regions in the optical imaging system. Further, on the image pickup device a micro lens or a light shielding mask is disposed off centered corresponding to each pixel of the plurality of pixel pairs for focus detection.
Using such an image pickup device will obviate the need of a sensor for focus detection and an optical system for the sensor besides an image pickup device for photographing.
When the defocus quantity is large, although a narrow focus detection region is used to avoid miss detection due to near/far conflict in the apparatus relating to the above described proposal, it is desirable to use a wide focus detection region. The near/far conflict refers to a case where when a far object and a near object are located on substantially the same optical axis, there may be confusion regarding to which of them the focus is adjusted.